Personal care products in the form of disposable absorbent articles are broadly available. Such products can include, for example, disposable diapers, adult incontinence briefs, panty liners, sanitary napkins, and the like. Such articles are generally worn in contact with or in proximity to the human body and can be used for the collecting and retaining of exuded body fluids.
Typically, personal care products in the form of absorbent articles comprise multiple fluid handling or contacting members or elements. At least one such member will be primarily designed to store liquid, and at least one other member will be primarily designed to acquire and/or distribute liquid.
The storage member used in such products and articles will often comprise super-absorbent material, which is admixed with the traditionally used pulp fiber material. Such super-absorbent materials can absorb many times (e.g., 10 or more times) their own weight in liquid. Modern products employ high concentrations of super-absorbent materials, that is concentrations in excess of 50% of the total weight of the storage member. These products achieve a high absorbing capacity with a very thin storage member and are accordingly typically overall thin products. While super-absorbent materials can store very large amounts of liquid, they are often not able to distribute the liquid from the point of impact to more remote areas of the absorbent article. Further, these types of storage members cannot acquire and absorb liquid as fast as liquid is received by the absorbent article.
Given the foregoing fluid handling characteristics of absorbent article storage members, acquisition/distribution layer (ADL) elements are often also used in absorbent articles. ADLs are members or elements which provide for the interim acquisition of large amounts of liquid and which often also allow for the relatively rapid distribution of that acquired liquid. The ADL thus plays a key role in using the whole absorbent capacity provided by the storage member.
In some instances, an ADL can be a sub-layer in an absorbent article, arranged between a topsheet and an absorbent storage core for holding fluid. The primary function of such an ADL is to transport fluid inputs from the outer surface of the absorbent article, such as a diaper or a feminine hygiene product, to the inner absorbent core, thereby imparting fast strikethrough and low rewet. To achieve these properties, the ADL design is typically a bulky, open-structured, resilient, fibrous nonwoven structure offering good compression recovery regaining its loft quickly after compaction.
Configurations for absorbent article ADLs have historically been nonwoven fibrous structures or webs comprising natural and/or synthetic fibers. These structures can be prepared by such techniques as wet-laying or dry-laying, e.g., air-laying, carding or combinations thereof. Such structures are then typically chemically consolidated or bonded by applying or infusing an emulsion copolymer, i.e., a latex, onto or into the structure and by subsequently curing the latex-containing structure to form the consolidated ADL.
Emulsion copolymers in latex form which have been used in ADL manufacture include styrene-butadiene-rubber (SBR) copolymers, acrylic-based copolymers and copolymers based on vinyl esters such as vinyl acetate. Latex ADL binders of these several types are disclosed, for example, in U.S. Patent Publication Nos. 2004/0242106; 2004/0103970; 2003/0089043 and 2003/0003830.
Body fluids, such as urine, which are acquired by, distributed through, and absorbed and stored by personal care products in the form of absorbent articles are generally alkaline liquids. Such alkaline liquids within the absorbent article can promote bacterial growth and ammonia generation which can, in turn, create problems of odor and skin irritation, i.e., diaper rash, for the wearer of the article. For this reason, pH neutralizing agents are frequently added to the absorbent cores, or even topsheets, of articles such as diapers in an effort to minimize odor and skin irritation problems.
Even if pH lowering additives are present in absorbent article absorbent cores or topsheets, existing commercially available ADL structures which also may be incorporated into such articles do not reduce the alkalinity of body fluids, such as urine, being distributed through such ADL structures. In fact, ADLs which are adhesively bonded using some types of consolidation chemistries may actually exacerbate fluid alkalinity problems. For example, SBR or acrylic emulsion copolymers, when used as ADL binders, require alkaline pH for good machine runnability during nonwoven ADL production. These types of emulsion copolymers are typically supplied at neutral or alkaline pH and often require post-addition of alkali, e.g., ammonia, to achieve good mechanical stability. The very nature of emulsion copolymers of this type renders them ineffective at reducing urine alkalinity, and they can furthermore destabilize if used in the presence of acidulants.
Given the foregoing considerations, it would be advantageous to identify additional types of ADL structures which utilize consolidation/bonding additives that can actually impart a pH lowering/alkalinity neutralizing effect to the ADL structure. ADLs employing such consolidation/bonding chemistry could thus serve to desirably lower the pH/alkalinity of body fluids passing through the ADL before the fluid reaches the absorbent storage core. This, in turn, could eliminate, or at least reduce, the need to incorporate significant amounts of pH/alkalinity control agents into the absorbent article core or topsheet, thereby simplifying the manufacture and converting of such articles.